I love turning over rocks in the intertidal zone – you never know what you might find!

Horse Clam (Tresus sp.) Siphon Extended
Horse Clam (Tresus sp.) with its siphon extended.

This rather suggestive looking image is the siphon of a Horse Clam (Tresus sp.) that I found underneath a rock at Florencia Bay in Pacific Rim National Park Reserve. I usually see just the tip of the siphon (see photo below – the clam retracted its siphon after I touched it) or the squirt of water when it withdraws under the sand when disturbed.

Horse Clam (Tresus sp.) Siphon Retracted
Horse Clam (Tresus sp.) with its siphon partially retracted.

This is one of two species of Horse Clam – either the Fat Gaper (Tresus capax) or the Pacific Gaper (Tresus nuttallii). Both are large clams, reaching up to 9″ (23 cm) in length and weighing up to 3 lbs (1.4 kg) or more. Empty shells found on the beach will have a very noticeable spoon like depression called a chondrophore at the hinge.

My reference books give opposite information on siphon colour. Rick Harbo’s Shells and Shellfish of the Pacific Northwest states that rim of the siphon of the Pacific Gaper tends to be tan to pale orange while the rim of the siphon of the Fat Gaper tends to be greenish in colour. Andy Lamb’s Marine Life of the Pacific Northwest suggests the reverse.

Since I can’t really make out the siphon rim colour and didn’t look too closely when I photographed it I think I’m just going to call this clam a Horse Clam and leave it at that!